This invention relates to a process for the polymerization of ethylene or .alpha.-olefins for providing polymers with an improved particle size distribution and a high stereoregularity, and a catalyst therefor.
The most typical Ziegler catalysts which are used for the polymerization of ethylene or .alpha.-olefins comprises a titanium compound-containing catalyst component and an organoaluminum compound.
It is well-known that a catalyst activity is improved by pulverizing a titanium catalyst component such as titanium trichloride and its compositions (for example, Japanese Patent Publication Nos. 14125/60 and 24271/64), by copulverizing the titanium component with various modifiers (for example, Japanese Patent Publication Nos. 24270/64, 24272/64, 10065/68, British Pat. No. 1087314, U.S. Pat. No. 3764591, Japanese Application Kokai Nos. 48-68497, 48-29694, 48-38295 and 49-53196), or by subjecting these pulverized products to a modification treatment of contacting with an organic solvent or a mixture thereof with a modifier and separating (for example, U.S. Pat. No. 3850899, Japanese Patent Publication Nos. 48638/74, 17319/75, 48637/74 and British Pat. No. 1370559).
With these treatments the catalyst performance is improved to some degree, but they have various disadvantages. For example, a polymerization activity is improved but a stereoregularity is lowered, or both of the polymerization activity and stereoregularity are improved but a particle size distribution of the titanium catalyst component is broadened. Particularly, when pulverized products of the starting titanium component are subject to the modification treatment with organic solvents, they are divided to fine particles and broadened in the particle size distribution, in which more than 10% by weight of the particles has a size smaller than 5 microns.
When homopolymerization or copolymerization of ethylene or .alpha.-olefins is carried out using Ziegler type catalysts comprising a titanium component and an organoaluminum compound, the particle size of the resulting polymer or copolymer is markedly influenced by the particle size of the titanium component used.
Thus, when using the modified titanium component having a wide particle size distribution, in which fine particles are included in large quantities, the resulting homopolymers or copolymers have also a wide particle size distribution, in which fine powders of less than 50 microns are usually included in an amount of 10 to 30% by weight.
When the polymers obtained have a wide particle size distribution and particularly, contain a large amount of fine powders, separating of the polymers from a solvent by filtrating or centrifuging encounters a difficulty and further, owing to scattering of the polymer fine powders in the drying and pelletizing steps, the loss of polymers increases.
Thus, superfluous equipments must be provided for overcoming such disadvantages and the production of polymer must be conducted by complicated process. Therefore improvement has been required.
Various methods for improving a catalyst performance have been proposed as mentioned above. Among them the modification treatment of the starting titanium component by various modifiers is disclosed, for example, in U.S. Pat. No. 3850899, Japanese Patent Publication No. 48638/74 and British Pat. No. 1370559.
As set forth in Comparative Examples given hereinafter, these methods are effective to some degree with respect of improvements in the catalyst activity, however, during the modification treatment the titanium component is divided to fine particles so that the preparation of polymer in a commercial scale encounters difficulties as mentioned above.